Self aligned patterning with multiple resist layers

ABSTRACT

A method for using self aligned multiple patterning with multiple resist layers includes forming a first patterned resist layer onto a substrate, forming a spacer layer on top of the first patterned resist layer such that spacer forms on side walls of features of the first resist layer, and forming a second patterned resist layer over the spacer layer and depositing a masking layer. The method further includes performing a planarizing process to expose the first patterned resist layer, removing the first resist layer, removing the second resist layer, and exposing the substrate.

PRIORITY DATA

The present application is a continuation of U.S. application Ser. No.13/757,137, filed Feb. 1, 2013, which is incorporated herein byreference in its entirety.

BACKGROUND

When fabricating integrated circuits, various features such as metallines are formed into and onto a semiconductor substrate. To form thesefeatures, photo-masks are used to form a pattern into a photo-resistlayer. The regions where the photo-resist layer is removed expose theunderlying substrate to an etching process used to form trenches wheremetal is subsequently placed.

As the patterns formed into photo-resist layers become increasinglydense, it becomes difficult to use a single photo-mask to form a patternin the photo-resist layer because features within the nanometer rangeare smaller than the resolution of a light source to which thephoto-resist layer is exposed. Thus, multiple masks may be used to formthe features within a pattern. Specifically, each of the multiple masksis used to create different features within the final pattern.

When multiple masks are used to form a single pattern, it is importantthat the masks are aligned properly so that various errors may beavoided. For example, it is problematic if two adjacent features, eachfrom a different mask, are formed too close to each other. Such errorsmay cause short circuits or bad circuit connections.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIGS. 1A-1B are diagrams showing illustrative multiple patterning,according to one example of principles described herein.

FIG. 2A-2H are diagrams showing an illustrative process for forming anintegrated circuit using self aligned patterning with similar mask tonetypes, according to one example of principles described herein.

FIG. 3A-3F are diagrams showing an illustrative process for forming anintegrated circuit using self aligned patterning with different masktone types, according to one example of principles described herein.

FIG. 4 is a flowchart showing an illustrative method for using selfaligned multiple patterning with multiple resist layers, according toone example of principles described herein.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the disclosure. Specific examples of components and arrangements aredescribed below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Moreover,the performance of a first process before a second process in thedescription that follows may include embodiments in which the secondprocess is performed immediately after the first process, and may alsoinclude embodiments in which additional processes may be performedbetween the first and second processes. Various features may bearbitrarily drawn in different scales for the sake of simplicity andclarity. Furthermore, the formation of a first feature over or on asecond feature in the description that follows may include embodimentsin which the first and second features are formed in direct contact, andmay also include embodiments in which additional features may be formedbetween the first and second features, such that the first and secondfeatures may not be in direct contact.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. For example, if the device in the figures is turned over,elements described as being “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the exemplary term “below” can encompass both an orientation ofabove and below. The apparatus may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein may likewise be interpreted accordingly.

FIGS. 1A-1B are diagrams showing illustrative multiple patterning 100.As mentioned above, as the density of integrated circuits increases,some features may be too close together for the resolution of aphoto-mask. To overcome this issue, the features of the pattern can beassigned to two or more masks.

FIG. 1A illustrates features 102 assigned to a first mask and features104 assigned to a second mask. In this example, feature 102-1 is tooclose to features 104-1 and 104-2. Thus, a single photo-mask would notbe able to form such a pattern. By putting features 104-1 and 104-2 on asecond mask, the appropriate pattern can be formed onto a photo-resistlayer. When patterning the features 104 assigned to the second mask, itis important that they are aligned properly so as not to come too closeto the features 102 formed by the first mask.

FIG. 1B is a diagram showing an illustrative top view 120 of selfaligned patterning. According to the present example, the features 106assigned to the first mask are formed first. A spacer 108 material isthen formed on and around the features 106. This spacer 108 ensures thatother features cannot be placed within a specific distance from thefeatures 106. For example, features 110, shown in phantom, are from asecond mask. The features 110 assigned to the second mask can bedeposited on top of the substrate and the spacer. Thus, any alignment oroverlay error will not bring the second mask features 110 unacceptablyclose to the features 106 from the first mask. As a result, the features110 will form the features 104, shown in FIG. 1A. The followingdescribes this self alignment process in further detail.

FIG. 2A-2H are diagrams showing an illustrative process for forming anintegrated circuit using self aligned patterning in which the two masksused to form two resist layers have the same type of tone. FIG. 2Aillustrates features 206 of a first patterned resist layer 204 beingformed. According to the present example, various features 206 areformed onto a substrate 202. In one example, the features are formedusing standard photolithographic techniques. Specifically, aphoto-resist layer is deposited onto the substrate 202. A mask is usedto expose certain regions of the resist layer to a light source. If themask used is a bright field mask, then the regions of the mask thatblock the light source define the features 206. A space 208 betweenfeatures 206 that is exposed to the light source becomes soluble to adeveloping solution and is removed.

FIG. 2B illustrates the deposition of a spacer layer over the substrate202. The spacer material is formed on the top and side walls of thefeatures 206. Because the features 206 are used to support the spacerlayer, the first patterned resist layer may be referred to as a mandrellayer. Various commonly used spacer materials may be used in accordancewith principles described herein. The spacer layer may be made from avariety of materials including, but not limited to, oxide, siliconnitride (SiN), titanium nitride (TiN), titanium dioxide (TiO₂), aluminumoxide (Al₂O₃), and tantalum nitride (TaN).

The thickness of the spacer material 210 may be based on the criticaldimension of the pattern. A critical dimension defines the minimumlength of a particular dimension that is deemed critical based on errortolerance. For example, the critical dimension may be the space betweentwo adjacent metal lines. The minimum space between the two lines may bedefined by a set of rules that are made to reduce errors in theintegrated circuit fabrication process to a tolerable level. By settingthe spacer thickness to at least the critical dimension distance, it canbe ensured that subsequently deposited features do not violate the rulesrelated to the critical dimension. Moreover, as will be discussedfurther below, a higher degree of overlay error can be tolerated.

FIG. 2C illustrates the deposition of a second patterned resist layer212. According to the present example, features of the final pattern aredefined by the features 214 of the second patterned resist layer 212.The final pattern refers to the pattern that results from both the firstmask and the second mask. In this example, the mask for the secondresist layer 212 is the same type of tone as the mask for the firstresist layer 204. Thus, features of the final pattern are defined byfeatures of both the first resist layer 204 and the second resist layer212. As is illustrated, the features 214 of the second patterned resistlayer 212 may overlap the spacer layer and even the features 206 of thefirst patterned resist layer 204. The overlap will not adversely affectthe intended final pattern. Thus, a larger alignment error between themasks that form the resist layers 204, 212 may be tolerated.

The second patterned photo-resist layer may be made from a variety ofstandard photo-resist materials. For example, the second patternedphoto-resist material may be a tri-layer that includes a bottom layerresist, a middle layer resist, and a top layer resist. The bottom layermay be a Bottom Anti-Reflective Coating (BARC) layer. The middle layermay be made of silicon and is used as a hard mask. The ArF immersionresist can be used for immersion lithographic patterning.

FIG. 2D illustrates the deposition of a masking layer 218. The maskinglayer 218 may be a standard hard mask material. For example, the maskinglayer material may be an ALD-Oxide material. The masking layer 218 fillsin the spaces between the features 214 of the second resist layer 212.

FIG. 2E illustrates a planarizing process 220 to grind away at eachlayer until the features of the first resist layer 204 are exposed. Theplanarizing process may be, for example, a Chemical Mechanical Polish(CMP) process. After such a process, the features of the second resistlayer 212, certain regions of the spacer material 210, and certainregions of the hard mask layer 218 will be exposed. FIG. 2F illustratesa removal process 222 to remove the resist layers 204, 212.Specifically, the removal process 222 selectively removes the resistmaterial that forms the first resist layer and the resist material ofthe second resist layer 212. The removal process does not, however,remove the spacer layer material 210 or the masking layer material 218To remove the first resist layer material 204, a dry etch process may beused. If the first resist layer material 204 is made of a carbonmaterial, then a O2/N2H2 ash may be used to remove the material.

FIG. 2G illustrates a further removal process 124 to remove the spacerlayer to expose the substrate 202 underneath. In one example, theremoval process 224 removes a small part of the spacer layer. Theremoval process 224 is designed so that a small part of the spacer layerthat is adjacent to the substrate is removed while the other layersremain substantially unaffected. For example, a removal process thatremoves a little bit from each layer may be used. Such a removal processcan be applied long enough to remove the thin spacer layer that isadjacent to the substrate. While this process will remove a little bitfrom each of the other layers, it won't be enough to substantiallyaffect the utility of such layers. After this removal process 224 isperformed and the substrate is exposed. The remaining materials act asthe final hard mask. Various lithographic processes may subsequently beperformed on the substrate. For example, the regions of the substratenot protected by the final hard mask may be etched away to form trenchesinto the substrate. These trenches may then be filled with a metalmaterial to form metal lines.

FIG. 2H illustrates an etching process 236 to form trenches 234 into thesubstrate after the final mask has been completed. In some examples,these trenches 234 may be subsequently filled in with metal to formmetal lines within the substrate. In one example, a dry etching processwith a CxFy base may be used. Through use of principles describedherein, a self aligned double pattern final hard mask is created. Thismay be done in fewer steps and tolerate more alignment error than othermethods.

The final features formed into the substrate after the final hard maskis complete are defined as follows. The trenches are defined by thefeatures of the first resist layer 204 and the features of the secondresist layer 212. Additionally, the space between features of the finalpattern is defined by the spacer material and the hard mask materialthat is filled in between the features of the second resist layer 212.

Thus, the final hard mask includes spaces 226 formed by the features 206of the first patterned resist layer 204, spaces 228 formed by features214 of the second patterned resist layer 212, and areas between spacesformed by the spacer layer 230 or by regions 232 where the masking layer218 was deposited between features 214 of the second patterned resistlayer 212.

FIG. 3A-3F are diagrams showing an illustrative process for forming anintegrated circuit using self aligned patterning in which the two masksthat form two different resist layers use a different type of tone. Thematerials and etching process used in the following process may besimilar to those of the above mentioned process. According to thepresent example, the first steps are as illustrated in FIGS. 2A-2B. Theprocess differs in that the masking layer is deposited before the secondresist layer is formed.

FIG. 3A is a diagram showing the deposition of a masking layer 302before formation of the second patterned resist layer. The masking layer302 may be made from the same type of material as the masking layerdiscussed above in FIGS. 2A-2H. The masking layer 302 is made of amaterial that can be selectively etched from the spacer material 219.

FIG. 3B is a diagram showing the formation of a second patterned resistlayer 304 on top of the masking layer 302. In the present example, themask used to pattern the second resist layer 304 is of a different masktone type than the mask used to pattern the first resist layer 204. Forexample, in this case, the space 308 between regions 306 of resistmaterial that remain after the second resist layer 304 has beenpatterned to define the features of the final pattern to be formed intothe underlying substrate 202.

FIG. 3C is a diagram showing a removal process 310 used to removeregions of the masking layer that are not protected by the secondpatterned resist layer 304. Thus, the removal process 310 selectivelyremoves the hard mask material that forms the masking layer 302 whileleaving the second resist layer material intact.

FIG. 3D is a diagram showing a removal process 312 used to remove thesecond resist layer 304. This removal process 312 is designed toselectively remove the second resist layer material while not removingthe masking layer material or the spacer layer material.

FIG. 3E is a diagram showing a planarizing process 314 used to removeeach layer to expose the features 206 of the first resist layer. FIG. 3Fis a diagram showing an illustrative removal process 316 to remove thefirst resist layer material. Additionally, the thin layer of spacermaterial on the substrate is removed to expose the substrate.

FIG. 3F illustrates the final hard mask pattern. The spaces in the hardmask pattern include spaces 318 resulting from the features 206 of thefirst resist layer 204 and spaces 320 resulting from spaces 308 in thesecond resist layer 304. Additionally, the regions between spacesinclude regions 322 resulting from the spacer layer and regions 324where the features 306 of the second resist layer 304 protected themasking layer 302.

Thus, using the process described above in accordance with FIG. 3, thesame final hard mask pattern that was formed by the process described inaccordance with FIG. 2 is achieved. If such a hard mask pattern is usedto form trenches for metal lines, then the metal lines are defined bythe features of the first patterned resist layer and the space betweenfeatures of the second patterned resist layer. Additionally, the spacebetween metal lines is defined by the spacer layer and the features ofthe second patterned resist layer. Again, a larger alignment error maybe tolerated without adversely affecting the pattern.

FIG. 4 is a flowchart showing an illustrative method 400 for using selfaligned multiple patterning using multiple resist layers. According tothe present example, the method includes a step of forming 402 a firstpatterned resist layer onto a substrate. The method also includes a stepof forming 404 a spacer layer on top of the first patterned resist layersuch that spacer forms on side walls of features of the first resistlayer. The method also includes a step of forming 406 a second patternedresist layer over the spacer layer and depositing a masking layer. Themethod also includes a step of removing 408 the first resist layer. Themethod also includes a step of removing 410 the second resist layer. Themethod also includes a step of exposing 412 the substrate.

According to certain illustrative examples, a method for using selfaligned multiple patterning with multiple resist layers includes forminga first patterned resist layer onto a substrate, forming a spacer layeron top of the first patterned resist layer such that spacer forms onside walls of features of the first resist layer, and forming a secondpatterned resist layer over the spacer layer and depositing a maskinglayer. The method further includes removing the first resist layer,removing the second resist layer, and exposing the substrate.

According to certain illustrative examples, a method for forming afabricated circuit includes forming a first patterned resist layer ontoa substrate, forming a spacer layer on top of the first patterned resistlayer such that spacer forms on side walls of features of the firstresist layer, forming a second patterned resist layer over the spacerlayer, and depositing a masking layer on the second resist layer. Themethod further includes performing a planarizing process to expose thefirst patterned resist layer, removing the first resist layer and thesecond resist layer, and exposing the substrate.

According to certain illustrative examples, a method for forming afabricated circuit includes forming a first patterned resist layer ontoa substrate, forming a spacer layer on top of the first patterned resistlayer such that spacer forms on side walls of features of the firstresist layer, and depositing a masking layer on the spacer layer. Themethod further includes forming a second patterned resist layer on themasking layer, etching away regions of the masking layer not covered bythe second resist pattern features, removing the second resist layer,performing a planarizing process to expose the first patterned resistlayer, removing the first resist layer, and exposing the substrate.

It is understood that various different combinations of the above-listedembodiments and steps can be used in various sequences or in parallel,and there is no particular step that is critical or required.Additionally, although the term “electrode” is used herein, it will berecognized that the term includes the concept of an “electrode contact.”Furthermore, features illustrated and discussed above with respect tosome embodiments can be combined with features illustrated and discussedabove with respect to other embodiments. Accordingly, all suchmodifications are intended to be included within the scope of thisinvention.

The foregoing has outlined features of several embodiments. Those ofordinary skill in the art should appreciate that they may readily usethe present disclosure as a basis for designing or modifying otherprocesses and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those of ordinary skill in the art should also realize that suchequivalent constructions do not depart from the spirit and scope of thepresent disclosure, and that they may make various changes,substitutions and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A method comprising: forming a first patternedresist layer over a substrate; forming a spacer layer over the firstpatterned resist layer such that the spacer layer covers the firstpatterned resist layer; forming a second patterned resist layer over thespacer layer; forming a hard mask layer over the second patterned resistlayer; and removing a first portion of the second patterned resist layerand a portion of the spacer layer to expose the first patterned resistlayer, wherein a second portion of the second patterned resist layer isdisposed over the substrate after removing the first portion of thesecond patterned resist layer.
 2. The method of claim 1, wherein formingthe spacer layer over the first patterned resist layer such that thespacer layer covers the first patterned resist layer includes formingthe spacer layer directly on the first patterned resist layer.
 3. Themethod of claim 1, wherein removing the first portion of the secondpatterned resist layer and a portions of the spacer layer to expose thefirst patterned resist layer further includes removing a portion of thehard mask layer to form a patterned hard mask layer.
 4. The method ofclaim 3, further comprising etching the spacer layer to form a patternedspacer layer by using the patterned hardmask as a mask.
 5. The method ofclaim 4, further comprising etching the substrate while using thepatterned hardmask and the patterned spacer layer as a mask.
 6. Themethod of claim 1, wherein forming the second patterned resist layerover the spacer layer includes forming the second patterned resist layerover the first patterned resist layer such that portion of the secondpatterned resist layer overlaps a portion of the first patterned resistlayer.
 7. The method of claim 1, wherein removing the first portion ofthe second patterned resist layer and a portion of the spacer layer toexpose the first patterned resist layer includes performing a chemicalmechanical polishing process.
 8. A method comprising: forming a firstpatterned resist layer over a substrate; forming a spacer layer coveringthe first patterned resist; forming a masking layer over the spacerlayer; forming a second patterned resist layer over the masking layer;etching the masking layer while using the second patterned resist layeras a mask; removing a portion of the spacer layer to expose the firstpatterned resist layer; removing the first patterned resist layer; andetching the substrate while using the masking layer and the spacer layeras a mask.
 9. The method of claim 8, further comprising removing thesecond patterned resist layer prior removing the portion of the spacerlayer to expose the first patterned resist layer.
 10. The method ofclaim 8, wherein forming the spacer layer covering the first patternedresist includes forming the spacer layer such that it defines a recess,and wherein forming the masking layer includes forming the masking layerwithin the recess.
 11. The method of claim 10, wherein the masking layeris recessed within the recess such that a top portion of the recess isunfilled by the masking layer after forming the masking layer over thespacer layer.
 12. The method of claim 11, wherein forming the secondpatterned resist layer over the masking layer includes forming thesecond patterned resist layer within the portion of the recess.
 13. Themethod of claim 10, wherein the masking layer is disposed within therecess when etching the substrate while using the masking layer and thespacer layer as the mask.
 14. The method of claim 8, wherein removingthe portion of the spacer layer to expose the first patterned resistlayer further includes removing another portion of the spacer layer toexpose the substrate.
 15. A method comprising: forming a first resistlayer over a substrate; forming a dielectric layer over the first resistlayer such that dielectric layer covers the first resist layer; forminga second resist layer over the dielectric layer; removing a portion ofthe dielectric layer to expose the first resist layer; and removing thefirst resist layer; and etching the substrate while using the dielectriclayer as a mask.
 16. The method of claim 15, wherein the first resistlayer and the second resist layer are formed using a different type ofmask tone.
 17. The method of claim 15, wherein removing the removing thefirst resist layer includes removing the second resist layer afterremoving the portion of the dielectric layer to expose the first resistlayer.
 18. The method of claim 15, further comprising forming a maskinglayer over the second resist layer.
 19. The method of claim 15, whereinafter removing the first resist layer the substrate is free of the firstresist layer.
 20. The method of claim 15, wherein removing the portionof the dielectric layer to expose the first resist layer includesremoving a first portion of the second resist layer to expose the firstresist layer, and wherein a second portion of the second resist layer isdisposed over the substrate after removing the first portion of thesecond resist layer.